/Engine/Source/Runtime/Slate/Public/Widgets/Views/SListView.h
Set the current selection mode of the list. If going from multi-select to a type of single-select and one item is selected, it will be maintained (otherwise all will be cleared). If disabling selection, any current selections will be cleared.
void SetSelectionMode ( const [TAttribute](API\Runtime\Core\Misc\TAttribute)< [ESelectionMode::Type](API\Runtime\Slate\Framework\Views\ESelectionMode__Type) > & NewSelectionMode )